JP5839135B2 - Spherical optical system and imaging device - Google Patents

Description

The present invention relates to an omnidirectional optical system and an imaging apparatus .

  2. Description of the Related Art An imaging system that uses a plurality of wide-angle lenses is known as an imaging system that “images the entire celestial sphere”. A wide-angle lens used in this type of imaging system is often “different in the magnification ratio between the lens center and the lens periphery”, unlike an imaging lens for normal planar imaging.

  When constructing a compact imaging system with “uniform image quality over the entire celestial sphere” using a known wide-angle lens, the imaging performance of the wide-angle lens is lower than that of the lens center. In order to compensate for “degradation of image quality easily at the periphery of the lens”, it is necessary to make the imaging magnification at the periphery “higher than the center of the lens”.

In general, it is known that a lens system in which the magnification around the lens is larger than the center of the lens, that is, a lens system in which the magnification per unit angle of view monotonously increases is “short as the total length of the lens system”. Since the thickness of the lens constituting the lens is reduced, the processability of the lens is deteriorated.
Contrary to the above, with a lens that takes into account the processability of the lens, the “magnification at the lens periphery is low compared to the lens center”, and the imaging magnification at the periphery is “higher than the lens center”. Then, the total length of the lens system tends to be long.

  Patent Document 1 discloses that the magnification at the periphery of an image is increased by bringing the projection method of a “fisheye lens” as a wide-angle lens close to the “stereoscopic projection method”.

An object of the present invention is to realize a novel imaging apparatus capable of capturing an image with uniform image quality over the entire imaging range, and a novel omnidirectional optical system used therefor.

  The imaging system according to the present invention is an “imaging system having a combination of a plurality of imaging optical systems” and has the following characteristics.

  The imaging optical system is configured by combining “one imaging optical system and one solid-state imaging device”.

  The “solid-state imaging device” is a “two-dimensional solid-state imaging device” in which a light receiving region forms an area area, and converts light collected by an imaging optical system to be combined into an image signal.

  The “imaging optical system” forms an image to be imaged on the light receiving region of the solid-state image sensor. This imaging optical system has “a total angle of view greater than 360 / n: A (degrees)” where n is a natural number of 2 or more.

  The magnification per unit angle of view is “monotonically increasing from angle of view: 0 (degrees) to 360 / n (degrees), and after exceeding the angle of view: 360 / n (degrees), the total angle of view: A (degrees). ), The rate of increase of the magnification decreases monotonously. That is, the imaging optical system is designed and manufactured so that the “magnification per unit angle of view” has such characteristics.

  Since the angle of view exceeds 360 / n (degrees) until the total angle of view: A (degrees), “the rate of increase in magnification per unit angle of view decreases monotonously”, so the angle of view is 360 / n (degrees). In the region from exceeding the total angle of view: A (degrees), the “magnification per unit angle of view” is as follows.

  In other words, compared to an increase in magnification up to 360 / n (degrees), the “gradual increase” state where the degree of increase is small, or a constant state (maintenance value per unit angle of view at 360 / n degrees is maintained. Or the magnification is “monotonically decreasing”.

  The projection method in which the magnification per unit angle of view increases monotonously with the angle of view is the “stereoscopic projection method”. Therefore, the image forming optical system is “stereoscopic projection from angle of view: 0 (degree) to 360 / n (degree)”, and “change in magnification per unit angle of view” in a larger angle of view area. The state becomes a slowly increasing state or a constant or monotonously decreasing state that does not change.

According to the omnidirectional optical system of the present invention, the 3D projection method can be applied over the entire angle of view while ensuring “a thickness that can be easily processed” in the peripheral portion of the wide-angle lens constituting the omnidirectional optical system. Compared to realization, the imaging optical system can be designed and manufactured easily and can be manufactured at low cost.

Omnidirectional type optical system according to claim 1, full angle of view: A is 180 degrees greater than the imaging optical system, a two-dimensional converting the light condensed by the imaging optical system into an image signal A combination of two imaging optical systems configured with a solid-state imaging device can be used as an omnidirectional imaging apparatus that captures an imaging target within a solid angle of 4π radians.

As described above, according to the present invention, a novel omnidirectional optical system and omnidirectional imaging device can be realized. The image forming optical system constituting the omnidirectional optical system does not have the magnification per unit angle of view “monotonically increasing over the entire angle of view of the image forming lens” but an image exceeding the angle of view: 360 / n. In the corner area, “slow increase, constant, or monotonous decrease”. Compared to the case where the stereoscopic projection system is realized over the entire angle of view while ensuring “thickness that can be easily processed” in the peripheral part of the wide-angle lens. Thus, the imaging optical system can be easily designed and manufactured, and can be manufactured at low cost. Therefore, an omnidirectional imaging device using such an imaging optical system can be realized at low cost.

It is a figure which shows an example which combined two imaging optical systems in the omnidirectional imaging system. It is a spherical aberration diagram of one embodiment of a wide-angle lens that is an imaging optical system. It is a field curvature figure of the Example of a wide angle lens. It is a coma aberration figure of the Example of a wide angle lens. It is a MTF characteristic figure of the Example of a wide angle lens. It is a MTF characteristic figure of the Example of a wide angle lens. It is a figure for demonstrating the change of the magnification per unit field angle of the Example of a wide angle lens. It is a figure which shows the characteristic of the Example of a wide angle lens. It is a figure for demonstrating one Embodiment of an omnidirectional imaging system. It is a figure for demonstrating another form of implementation of an omnidirectional imaging system.

  Hereinafter, embodiments will be described.

  FIG. 9 shows an example of an omnidirectional imaging system using two wide-angle lenses as one embodiment of the invention.

  In this example, two wide-angle lenses WLA and WLB are combined as “two imaging optical systems” so that information on the omnidirectional sphere can be imaged. The wide-angle lenses WLA and WLB are “of the same specification” and are combined in opposite directions so that their optical axes match.

  The image picked up by the wide-angle lens WLA is formed on the light receiving surface of the two-dimensional solid-state image pickup device SNA, and the image picked up by the wide-angle lens WLB is formed on the light receiving surface of the two-dimensional solid-state image pickup device SNB. These solid-state imaging devices SNA and SNB convert the received light distribution into “image signals” and input them to the image processing means 2.

  The image processing means 2 combines the image signals from the solid-state imaging devices SNA and SNB into one image to obtain a “solid angle: 4π radians image (hereinafter referred to as“ global image ”)”, a display, The image is output to the output unit 3 such as a printing apparatus, and the output unit outputs an omnidirectional image.

  In the wide-angle lenses WLA and WLB, n = 2, and these wide-angle lenses WLA and WLB have an angle of view exceeding 180 (= 360/2) degrees: A (degrees).

  The wide-angle lenses WLA and WLB monotonically increase in “magnification per unit angle of view” between the angle of view: 0 (degrees) to 180 (= 360/2) degrees, and the angle of view: 180 degrees to the total angle of view: Up to A degrees, the increase rate of the magnification is monotonously decreased.

  The technical significance of such a change characteristic of “magnification per unit angle of view” will be described.

  In a “two-dimensional solid-state image pickup device” such as the solid-state image pickup device SNA or SNB, extremely small light receiving regions are separated from each other on the light receiving surface, and are two-dimensionally arranged with “uniform high density”. Yes. Information that is photoelectrically converted in each minute light receiving area constitutes “pixel information of image information”.

  The wide-angle lenses WLA and WLB have their optical axes “positioned perpendicular to the center of the light-receiving area of the corresponding solid-state imaging device”, and the light-receiving area “is the imaging surface of the corresponding wide-angle lens”. As described above, the positional relationship with respect to the solid-state imaging devices SNA and SNB is determined.

  By the way, the imaging performance of the imaging lens generally decreases as the spatial resolution (MTF) decreases and the brightness of the image decreases as the distance from the optical axis increases on the imaging surface.

  “The spatial resolution (MTF) decreases as the distance from the optical axis on the image plane decreases, and the brightness of the image decreases.” This means that the image information given to “part” is “poor”.

  In order to compensate for such “deterioration of image information”, the “imaging magnification” may be increased toward the periphery of the light receiving region. That is, when the imaging magnification increases at the peripheral portion, the area on the light receiving surface that receives “constant image information” increases as the distance from the optical axis of the wide-angle lens increases. ”Increases, and the above“ deterioration of image information ”can be compensated.

  The imaging optical system (wide-angle lenses WLA and WLB) used in the “omnidirectional imaging system” shown in FIG. 9 has a full field angle in which “magnification per unit field angle” exceeds 180 degrees as described above: Of A, the angle of view increases monotonically from 0 degrees (optical axis) to 180 degrees, and the angle of magnification increases from 180 degrees to the total angle of view: A degrees. Configured.

  That is, from the angle of view: 180 degrees to the total angle of view: A degrees, the magnification per unit angle of view is “a moderate increase with an increase rate lower than the increase rate up to 180 degrees” or “unit angle of view at 180 degrees. It becomes a state of “a constant magnification for maintaining the magnification per hit” or “a monotonous decrease”.

  In the following, for the sake of concreteness of description, the “magnification per unit angle of view” from the angle of view: 180 degrees to the total angle of view: A degrees is “a constant magnification that substantially maintains the magnification per unit angle of view at 180 degrees”. Suppose that

  If the wide-angle lenses WLA and WLB are used alone, the “magnification per unit angle of view” is set to “all angles of view: toward A degree” in the entire angle of view range from 0 degrees to the entire angle of view: A degrees. It is preferable to increase monotonously.

  Referring to FIG. 9, the wide angle lenses WLA and WLB are combined as shown.

  In FIG. 9, the symbol “a1” is the vertex of the lens surface closest to the object side of the wide-angle lens WLA, and the symbol “c1” is the vertex of the lens surface closest to the object side of the wide-angle lens WLB.

The “incident light beams” incident on the wide-angle lenses WLA and WLB at the maximum angle of view “cross each other” at points b1 and d1 shown in FIG. The distance from the lens apexes a1 and c1 on the objective side of the wide-angle lenses WLA and WLB to the plane passing through the points b1 and d1 is the distance R1 shown in the figure.
The distance between the straight line connecting the lens vertices a1 and c1 (the optical axes of the wide-angle lenses WLA and WLB) and the points b1 and d1 is the distance L1 shown in the figure.

  In FIG. 9, the maximum field angle light beam incident on the wide angle lens WLA has a “conical shape” with the objective lens apex a1 as the apex, and the maximum field angle light beam incident on the wide angle lens WLB is also the object side lens apex. It is “conical” with c1 as the apex.

  Then, these two conical surfaces (bottom radius: L1, height: R1) are combined with a common lens optical axis “a space part surrounded by two conical surfaces (in FIG. 9, points a1 and b1). , C1 and d1, the inside of the spatial shape obtained by rotating the parallelogram around the straight line connecting the points a1 and c1) is a “space area not imaged”.

  Now, in FIG. 9, the incident light beams incident on the “field angle: a portion exceeding 180 degrees” of the wide-angle lenses WLA and WLB intersect with each other in the plane including the points b1 and d1, and the light rays incident at the angle of view A are , Points b1 and d1 intersect on a circumference having a diameter.

Accordingly, among the imaging light beams of the wide-angle lenses WLA and WLB, the “light beam having an angle of view between 180 degrees to the full field angle A” is imaged in common to both the solid-state imaging devices SNA and SNB. Will do.
That is, of the image formed by the wide-angle lens WLA on the solid-state image pickup device SNA, an image portion (referred to as “IA”) where an “angle of view: a luminous flux from 180 degrees to A degrees” is formed, and solid-state image pickup. An image portion (referred to as “IB”) on which an “angle of view: a luminous flux from 180 degrees to A degrees” forms an image on the element SNB by the wide-angle lens WLB is the same image.

Accordingly, when the image signals from the solid-state imaging devices SNA and SNB are combined to generate an omnidirectional image, the image portion IA received by the solid-state imaging device SNA and the image portion IB received by the solid-state imaging device SNB Therefore, if these image portions IA and IB are used, “double the amount of information” can be obtained for the same image portion.
In other words, by using two wide-angle lenses and a solid-state imaging device, the “light receiving area” is increased for an image in an angle of view region exceeding 180 degrees, which is the same per unit angle of view. It is the same as increasing the magnification.

  Therefore, even if the magnification per unit angle of view in the wide-angle lenses WLA and WLB is “substantially constant without increasing monotonously” in the portion where the angle of view exceeds 180 degrees, it is twice as large as that in these portions. Since the amount of information can be used, it is possible to obtain an image that is inferior to an image with an angle of view up to 180 degrees.

  In other words, only for the “peripheral lens peripheral part” where the images of the wide-angle lenses WLA and WLB are reduced, by reducing the magnification increase rate around the unit angle of view, the lens is more than necessary while ensuring the thickness necessary for lens processing. Prevents the total length from becoming longer.

  In the example described above, the magnification per unit angle of view in the wide-angle lenses WLA and WLB is substantially constant for portions exceeding 180 degrees, but the information on the image portions IA and IB can be used together. Not only in the case where the magnification is constant, it is sufficient that the magnification per unit angle of view gradually increases in a field angle region exceeding 180 degrees as well as “monotonically decreases”. The amount of information can be compensated, and “a omnidirectional image with uniform image quality over the entire celestial sphere” can be captured.

  In addition, since the image portions IA and IB are “same images”, when composing an image signal output from the solid-state imaging devices SNA and SNB to form an “omnidirectional image”, these image portions IA, Let IB be “reference data representing the same image” and “reference for image joining”.

  In the example described above, the “magnification per unit angle of view” of the wide-angle lenses WLA and WLB has been described. However, the above characteristics of the wide-angle lenses WLA and WLB may be specified by “relationship between image height and angle of view”. it can.

  That is, the differential of image height: Y by angle of view: θ: dY / dθ is the rate of change in image height per unit angle of view, and has a corresponding relationship with “change in magnification per unit angle of view”.

  When the angle of view becomes larger than 180 degrees, the “magnification increase rate” per unit angle of view decreases monotonically, and the magnification becomes “slowly increasing, constant, or monotonically decreasing”, differentiation: dY / dθ Decreases rapidly.

Differentiation: dY / dθ is the aforementioned condition:
(1) 43.3 ≧ dY / dθ ≧ 0.007 [mm / deg]
Is preferably satisfied.

  In a region where the angle of view is greater than 180 degrees and the rate of increase in magnification per unit angle of view decreases monotonously, the difference rapidly decreases: dY / dθ falls below the lower limit of 0.007 mm / deg. The images IA and IB become “over-compressed images”, which are insufficient as “reference data” that is used as a reference in image synthesis.

  Further, the upper limit is a limit due to “the size of the light receiving surface of the solid-state imaging device”. The maximum size of the light-receiving surface that is currently marketed as a solid-state image sensor is 35 mm full size. If this size is taken into consideration, the light-receiving surface size that can be adapted is exceeded if the upper limit of 43.3 is exceeded. A solid-state imaging device cannot be obtained.

  Thus, the upper limit of the condition (1) is regulated by the size of the light receiving surface of the solid-state imaging device. Therefore, if a solid-state imaging device having a “larger light receiving surface size” is realized in the future, the condition (1) ) Can be set larger.

  The example described above can be used in general cases.

  That is, n is a natural number greater than or equal to 2 and has a total angle of view greater than 360 / n: A (degrees), and “the magnification per unit angle of view is monotonous between 0 and 360 / n (degrees). An imaging optical system in which the angle of view increases monotonously from the angle of view: 360 / n (degrees) to the total angle of view: A (degrees), and the light condensed by the imaging optical system An image pickup system having a combination of n or more image pickup optical systems including a two-dimensional solid-state image pickup element that converts a signal into an image signal can be configured.

Further, the image height of the imaging optical system: the angle of view of Y: the differentiation by θ: dY / dθ is the condition:
(1) 43.3 ≧ dY / dθ ≧ 0.007 [mm / deg]
It is preferable to satisfy.

  For example, three wide-angle lenses (imaging optical system) having an angle of view greater than 360 degrees / 3 = 120 degrees: A (for example, 140 degrees) are arranged radially in the same plane, and a solid-state image sensor is provided for each. When combined to form an imaging system, a 360-degree horizontal panoramic image can be captured.

  The image obtained in this case is not a “spherical image”, but such an imaging system that can capture a horizontal panoramic image can be favorably implemented as an in-vehicle camera or a security camera.

  If the four-angle wide angle lens having the angle of view: A = 140 degrees is spatially radial and combined with a regular tetrahedron to form an omnidirectional imaging system, an omnidirectional image of solid angle: 2π radians can be obtained. Can be imaged.

  Alternatively, when an imaging system is configured by arranging four wide-angle lenses having an angle of view larger than 360 degrees / 4 = 90 degrees: A (for example, 100 degrees) radially in the same plane, and combining solid-state imaging elements with each of them. 360-degree horizontal panoramic image can be picked up. Eight image pickup optical systems by combining such a wide-angle lens and a solid-state image pickup device are radial in space, and combined with a regular octahedron type, an omnidirectional image pickup system And an omnidirectional image with a solid angle of 2π radians can be captured.

  FIG. 10 is a diagram showing another embodiment of the omnidirectional imaging system.

  In this example, two wide-angle lenses WLC and WLD are combined as “two imaging optical systems” so that information of the omnidirectional sphere can be imaged. The wide-angle lenses WLC and WLD have the same specifications, and are combined in opposite directions so that their optical axes match.

  The image picked up by the wide-angle lens WLC is formed on the light receiving surface of the two-dimensional solid-state image pickup device SNC, and the image picked up by the wide-angle lens WLD is formed on the light receiving surface of the two-dimensional solid-state image pickup device SND. These solid-state imaging devices SNC and SND convert the received light distribution into “image signals” and input them to the image processing means 2.

  The image processing means 2 combines the image signals from the solid-state image pickup devices SNC and SND into one image and outputs it to the output means 3 such as a display or a printing device as a omnidirectional image with a solid angle of 4π radians. The output means outputs a spherical image.

  The wide-angle lenses WLC and WLD are similar to the wide-angle lenses WLA and WLB described above in terms of optical functions, and have an angle of view: A degree exceeding 180 (= 360/2) degrees.

  In addition, the “magnification per unit angle of view” increases monotonically between the angle of view: 0 degrees to 180 degrees, and the magnification rate increases monotonously from the angle of view: 180 degrees to the full angle of view: A degrees. The image height: Y angle of view: differentiation by θ: dY / dθ satisfies the condition (1).

  In FIG. 10, the symbol “a2” is the vertex of the lens surface closest to the object side of the wide-angle lens WLC, and the symbol “c2” is the vertex of the lens surface closest to the object side of the wide-angle lens WLD.

The “incident light beams” incident on the wide-angle lenses WLC and WLD “cross each other” at the points b2 and d2 shown in the figure, and the points b2 and d2 from the lens vertices a2 and c2 on the objective side of the wide-angle lenses WLC and WLD. The distance from the plane passing through is a distance R2 shown in the figure.
The distance between the straight line connecting the lens vertices a2 and c2 (the object-side optical axes of the wide-angle lenses WLC and WLD) and the points b2 and d2 is the distance L2 shown in the figure.

  The maximum field angle light beam incident on the wide-angle lens WLC has a conical shape having the objective-side lens apex a2 as a vertex, and the maximum field-angle light beam incident on the wide-angle lens WLD is also a cone having the objective-side lens vertex c2 as a vertex. Is.

  These two conical surfaces (bottom radius: L2, height: R2) are combined with a common object-side optical axis. A parallelogram connecting points a2, b2, c2, and d2, points a2 and c2. The “inside of a spatial shape obtained by rotating around a connecting straight line” is a “space area that is not imaged”.

  When the embodiment of FIG. 10 is compared with the embodiment of FIG. 9, L2 <L1 and R2 <R1, and in the embodiment of FIG. 10, the “space area not imaged” is more than that of FIG. It is getting smaller.

  That is, the omnidirectional imaging system shown in FIG. 10 can capture omnidirectional images up to “closer regions” than those shown in FIG.

  This is because, in the omnidirectional imaging system of FIG. 10, the wide-angle lenses WLC and WLD, which are imaging optical systems, include a first lens group (having negative refractive power) on the object side and a second lens on the image side. The first lens group includes a “reflecting member that bends the optical path toward the second lens group”, and the optical path is bent 90 degrees within the lens. Thus, the distance (= 2R2) between the vertex a2 of the lens surface closest to the objective side of the first lens group of the wide-angle lens WLC and the vertex c2 of the lens surface closest to the objective side of the first lens group of the wide-angle lens WLD. ) Is “narrower” than 2R1 in FIG.

  As described above, the wide-angle lenses WLC and WLD, which are the imaging optical systems of the respective imaging optical systems, include the negative first lens group disposed on the object side and the positive second lens group disposed on the image side. Since the first lens group has a reflecting member that bends the optical path toward the second lens group, the imaging portion of the omnidirectional imaging system can be reduced in size, and the entire sky up to the “closer area” can be reduced. A spherical image can be obtained.

Hereinafter, a description will be given based on specific examples.
FIG. 1 is a diagram illustratively showing a main part of another embodiment of an omnidirectional imaging system.

  In FIG. 1, the portions indicated by reference signs A and B indicate “imaging optical systems”.

  Each of the two imaging optical systems A and B is constituted by “a wide-angle lens (imaging optical system) having an angle of view wider than 180 degrees and an imaging sensor that captures an image by the wide-angle lens”. The imaging sensor is a “two-dimensional solid-state imaging device”.

  The wide-angle lens of the imaging optical system A includes a “front group” configured by lenses LA1 to LA3, a right-angle prism PA that configures a reflecting member, and a “rear group” configured by lenses LA4 to LA7. An aperture stop SA is disposed on the object side of the lens LA4.

  The wide-angle lens of the imaging optical system B includes a “front group” composed of lenses LB1 to LB3, a right prism PB constituting a reflecting member, and a “rear group” composed of lenses LB4 to LB7. An aperture stop SB is disposed on the object side of the lens LB4.

In these wide-angle lenses, the “front group” and the right-angle prism form a “first lens group”, and the “rear group” forms a “second lens group”.
In the following description, the terms “front group, right angle prism, rear group” are used.

  The lenses LA1 to LA3 constituting the front group of the wide-angle lens of the imaging optical system A are, in order from the object side, a negative meniscus lens (LA1) made of a glass material, a negative lens (LA2) made of a plastic material, and a negative meniscus made of a glass material. This is the lens (LA3).

  The lenses LA4 to LA7 constituting the rear group are, in order from the object side, a biconvex lens (LA4) made of a glass material, a cemented lens of a biconvex lens (LA5) and a biconcave lens (LA6) made of a glass material, and a biconvex lens (LA7 made of a plastic material). ).

  The lenses LB1 to LB3 constituting the front group of the wide-angle lens of the imaging optical system B are, in order from the object side, a negative meniscus lens (LB1) made of a glass material, a negative lens (LB2) made of a plastic material, and a negative meniscus made of a glass material. This is the lens (LB3).

  The lenses LB4 to LB7 constituting the rear group are, in order from the object side, a biconvex lens (LB4) made of a glass material, a cemented lens of a biconvex lens (LB5) and a biconcave lens (LB6) made of a glass material, and a biconvex lens (LB7 made of a plastic material). ).

  In these imaging optical systems A and B, the negative lenses LA2 and LB2 made of the plastic material of the front group and the biconvex lenses LA7 and LB7 made of the plastic material of the rear group are “aspheric on both surfaces”. It is a spherical lens.

  The position of the front principal point in each wide-angle lens is set between the second lenses LA2 and LB2 and the third lenses LA3 and LB3.

  In the wide-angle lens of the imaging optical system A, the distance between the intersection between the optical axis of the front group and the reflecting surface and the front principal point is “d1” in FIG. 1, and the front-group light in the wide-angle lens of the imaging optical system B The distance between the intersection of the axis and the reflecting surface and the front principal point is “d2”.

When these distances “d1, d2” are “d”, “d” and the focal length: f are the conditions:
(2) 7.0 <d / f <9.0
By satisfying the above, the wide-angle lens can be made compact and the influence of parallax can be reduced.

  The right-angle prisms PA and PB are preferably formed of “a material having a refractive index of d-line greater than 1.8”. Since the prisms PA and PB “internally reflect” light from the front group toward the rear group, the optical path of the imaging light beam passes through the prism. When the material of the prism has a high refractive index as described above, the “optical optical path length” in the prism is longer than the actual optical path length, and the distance to bend the light beam can be increased. The “optical path length between the front group and the rear group” in the rear group can be made longer than the mechanical optical path length, and the wide-angle lens can be configured compactly.

  Further, by arranging the prisms PA and PB near the aperture stops SA and SB, a small prism can be used, and the distance between the wide-angle lenses can be reduced.

  The prisms PA and PB are disposed between the front group and the rear group. The front group of the wide-angle lens has a function of taking in light rays having a wide angle of view larger than 180 degrees, and the rear group effectively functions to correct aberrations in the formed image.

  By arranging the prisms as described above, they are less susceptible to prism misalignment and manufacturing tolerances.

Specific examples of the wide-angle lens shown in FIG.
The embodiment is a wide-angle lens used for the imaging optical systems A and B of the omnidirectional imaging system shown in FIG. 1, and is used for both the imaging optical systems A and B. That is, the two wide-angle lenses used in the imaging optical systems A and B have “same specifications”, and the distance shown in the figure: d1 = d2.
The distance: d1 is “the distance on the optical axis between the entrance pupil and the reflecting surface of the prism PA” of the wide-angle lens of the imaging optical system A, and the distance: d2 is “the entrance pupil and the distance of the wide-angle lens of the imaging optical system B”. The distance on the optical axis with respect to the reflecting surface of the prism PB.

  In the following, f is the focal length of the entire system, No is the F number, and ω is the angle of view.

  “Surface numbers” are sequentially 1 to 23 from the object side, and indicate a lens surface, a prism entrance / exit surface, a reflecting surface, a diaphragm surface, a filter surface and a light receiving surface of an image sensor.

  “R” is the radius of curvature of each surface, and “paraxial radius of curvature” for an aspherical surface.

  “D” is the surface separation, “Nd” is the refractive index of the d-line, and “νd” is the Abbe number. The object distance is infinite. The unit of the quantity having the dimension of length is “mm”.

"Example"
f = 0.75, No = 2.14, ω = 190 degrees Face number R D Nd νd
1 17.1 1.2 1.834807 42.725324
2 7.4 2.27
3-1809 0.8 1.531131 55.753858
4 * 4.58 2
5 * 17.1 0.7 1.639999 60.78127
6 2.5 1.6
7 ∞ 0.3
8 ∞ 5 1.834000 37.160487
9 ∞ 1.92
10 ∞ (aperture stop) 0.15
11 93.2 1.06 1.922860 18.896912
12-6.56 1.0
13 3.37 1.86 1.754998 52.321434
14-3 0.7 1.922860 18.896912
15 3 0.3
16 * 2.7 1.97 1.531131 55.753858
17 * -2.19 0.8
18 ∞ 0.4 1.516330 64.142202
19 ∞ 0
20 ∞ 0.3 1.516330 64.142202
21 ∞ 0.3
22 Imaging surface.

Aspherical
The surfaces marked with “*” in the above data (both surfaces of the second lens in the front group and both surfaces of the final lens in the rear group) are aspherical surfaces.

The aspherical shape is a reciprocal of the paraxial radius of curvature (paraxial curvature): C, height from the optical axis: H, conic constant: K, and the non-spherical coefficients of the above orders, where X is the non-axis in the optical axis direction. As a spherical quantity, the well-known formula X = CH ² / [1 + √ {1− (1 + K) C ² H ² }]
+ A4 · H ⁴ + A6 · H ⁶ + A8 · H ⁸ + A10 · H ¹⁰ + A12 · H ¹² + A14 · H ¹⁴
The shape is specified by giving a paraxial radius of curvature, a conic constant, and an aspherical coefficient.

  The aspherical data of the above example is given below.

Third side
4th: 0.001612
6th: -5.66534e-6
8th: -1.99066e-7
10th: 3.69959e-10
12th: 6.47915e-12
4th page
4th: -0.00211
6th: 1.66793e-4
8th: 9.34249e-6
10th: -4.44101e-7
12th: -2.96463e-10
16th page
4th: -0.006934
6th: -1.10559e-3
8th: 5.33603e-4
10th: -1.09372e-4
12th: 1.80753-5
14th: -1.52252e-7
17th page
4th: 0.041954
6th: -2.99841e-3
8th: -4.227219e-4
10th: 3.426519e-4
12th: -7.19338e-6
14th: -1.69417e-7
In the above aspherical notation, for example, “-1.69417e-7” means “-1.69417 × 10 ⁻⁷ ”.
“4th to 14th” is “A4 to A14”, respectively.

In the wide-angle lens of the example, “d1 = d2 = d = 6 mm”. Since f = 0.75 mm, d / f = 8, which satisfies the above condition (2).
Further, the distance from the lens surface closest to the object side to the reflecting surface of the right-angle prism: DA, the distance from the reflecting surface to the lens surface closest to the image side: DB,
DA = 8.87
DB = 14.76
The distance: D + DB while securing the “lens total length necessary for the performance of the wide-angle lens”, while making the distance: D1 shorter than D2, the distance between the “most object side lens surfaces” of the front group can be reduced. As in the example shown in FIG. 10, a “global image up to a closer distance” can be obtained by shortening the length.

  Note that the wide-angle lens of the above embodiment is combined as shown in FIG. 1 as compared with a case where a wide-angle lens that does not bend the optical path is used in parallel (R1 = 20 mm, L1 = 229 mm in the configuration shown in FIG. 9). In this case, R = 11 mm and L = 126 mm could be achieved.

In a wide-angle lens having an angle of view exceeding 180 degrees, the optical path length varies depending on the difference in lens thickness between the light beam passing through the center of the lens and the light beam passing through the periphery, leading to performance degradation.
In the wide-angle lens of the example, among the three lenses in the front group, the “second lens difference in the lens thickness between the vicinity of the optical axis and the periphery” tends to appear in the second lens. Therefore, correction is performed by using the second lens as a plastic lens and making both surfaces aspherical.

  Further, the last lens in the rear group is a plastic lens, and both surfaces thereof are aspherical so that “various aberrations occurring on the object side of this lens” can be corrected satisfactorily.

  Further, among the four lenses in the rear group, “chromatic aberration” is favorably corrected by cementing the second biconvex lens and the third biconcave lens.

  FIG. 2 shows a spherical aberration diagram of the wide-angle lens of the example. Further, FIG. 3 shows a view of the field curvature.

  FIG. 4 shows a coma aberration diagram.

  5 and 6 are diagrams showing the OTF characteristics. In FIG. 5, the horizontal axis represents “spatial frequency” in FIG. 5 and FIG. 6 represents the half angle of view in “degrees”.

  As is clear from these figures, the wide-angle lens of the example has extremely high performance.

  In the wide-angle lens of the embodiment, as described above, the “total angle of view” is 190 degrees larger than 180 degrees, and the “magnification per unit angle of view” monotonically increases from 0 to 180 degrees. Yes.

FIG. 7 illustrates the “angle of view spread on the light-receiving surface of the solid-state imaging device” due to a monotonically increasing magnification from 0 to 180 degrees.
“Same angle of view” is drawn in increments of 30 degrees until “view angle: 0 to 180 ° (half angle of view 0 to 90 °)”. As the angle of view increases, it can be seen that the sensor area (width of concentric circles) used by the solid-state imaging device is increased (see the size of the black circles in the figure). That is, in the range of angle of view: 0 to 180 degrees, the magnification per unit angle of view increases monotonously.
On the other hand, the range of the angle of view of 180 degrees to 190 degrees is such that the image is used as “the connection between the two captured optical systems”, and therefore the width of the concentric circle is larger than the sensor area used near the angle of view of 180 degrees. Is narrower. That is, the magnification per unit angle of view is small in this region.

FIG. 8 shows changes in “magnification per unit angle of view” and changes in dY / dθ of the wide-angle lens of the example. “Magnification per unit angle of view” is described as “projection method” in the figure.
The horizontal axis indicates the half field angle (0 to 100 degrees), the vertical axis indicates the right dY / dθ, and the left side indicates the image height (Y).

  As is clear from FIG. 8, in the wide-angle lens of the example, the magnification per unit angle of view monotonously increases from 0 to 90 degrees (= 360/2), and the rate of increase at a larger angle of view. Monotonically decreases and the degree of increase is moderate, and dY / dθ satisfies the condition (1).

  In the example described above, the two imaging optical systems (wide-angle lenses) used in the omnidirectional imaging system have “same specifications”. However, the present invention is not limited to this, and the optical characteristics are the same. If it is.

  Further, in order to combine images captured by a plurality of solid-state image sensors as one image, it is possible to connect adjacent images based on information on the positional relationship between the imaging optical systems. As in the example, “Angle of view: 180 ° to 190 °” can be used as reference data when joining the images, and this changes the relative positional relationship between the two imaging optical systems due to the ambient temperature. Can also "join images accurately".

  Further, by using a prism as the reflecting member as in the wide-angle lens of the embodiment, the reflecting member can have a function as a lens, and the width of the omnidirectional imaging system can be reduced.

A Imaging optical system
B Imaging optical system
LA1-LA7 lens
LB1-LB7 lens
PA, PB prism
SA, SB Aperture stop SNA, SNB, SNC, SND Solid-state image sensor

JP 2006-089442 A

Claims (2)

An omnidirectional optical system having a plurality of optical systems,
An angle of view area in which the subject images incident on the respective optical systems do not overlap each other in a stereoscopic projection method in which the magnification per unit angle of view monotonously increases with the angle of view;
Wherein an outer viewing angle area than viewing angle area of the stereoscopic projection system, the rate of increase in magnification per unit view angle monotonically decreases, omnidirectional optical comprising: a field angle region in which the object image is overlapped system. An imaging apparatus for imaging an imaging target within a solid angle of 4π radians using the omnidirectional optical system according to claim 1.

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